1. Field of the Invention
This invention generally relates to detecting defects on a wafer. Certain embodiments relate to assigning individual output in raw output for a wafer generated by an inspection system to different segments.
2. Description of the Related Art
The following description and examples are not admitted to be prior art by virtue of their inclusion in this section.
Wafer inspection, using either optical or electron beam technologies, is an important technique for debugging semiconductor manufacturing processes, monitoring process variations, and improving production yield in the semiconductor industry. With the ever decreasing scale of modern integrated circuits (ICs) as well as the increasing complexity of the manufacturing process, inspection becomes more and more difficult.
In each processing step performed on a semiconductor wafer, the same circuit pattern is printed in each die on the wafer. Most wafer inspection systems take advantage of this fact and use a relatively simple die-to-die comparison to detect defects on the wafer. However, the printed circuit in each die may include many areas of patterned features that repeat in the x or y direction such as the areas of DRAM, SRAM, or FLASH. This type of area is commonly referred to as an array area (the rest of the areas are called random or logic areas). To achieve better sensitivity, advanced inspection systems employ different strategies for inspecting the array areas and the random or logic areas.
To set up a wafer inspection process for array inspection, many currently used inspection systems require users to manually set up regions of interest (ROI) and apply the same set of parameters for defect detection in the same ROI. However, this method of set up is disadvantageous for a number of reasons. For example, as design rules shrink, region definition can be much more complicated and much smaller in area. With the limitations on stage accuracy and resolution of the inspection system, manual set up of ROI will become impossible eventually. On the other hand, if the distance between page breaks is larger than Fourier filtering can perform, the page break will not be suppressed in the array region.
In another method, intensity is used as a feature of segmentation to group similar intensity pixels together. Then, the same set of parameters is applied for the same group of pixels (intensity-based). However, this method also has a number of disadvantages. For example, an intensity-based segmentation algorithm can be used when a geometry feature scatters uniformly. Often, however, this is not enough. Therefore, other property-based segmentation is needed.
Accordingly, it would be advantageous to develop methods and systems for detecting defects on a wafer that can achieve better detection of defects by utilizing the knowledge that defects of interest and nuisance/noise reside in different segments geometrically.